Echo sounding indicator



E C N A m L T G ECHO SOUNDING INDICATOR Filed March l0, 1945 llllllll l l l I l I Il lll if".

George T. Lorance, Chappaqua, N. Y., assigner to International Projector Corporation, New York, N. Y., a corporation oi Delaware Application March 10, 1945, Serial No. 582,117

2 Cs. (Cl. 177-388) back to the vessel gives an indication of the depth oi the 'water under the vessel.

One object of the invention ls to provide -a light-weight and portable depth indicator which is suitable for war-time use in invasion barges and the like, and for peace-time use on fishing boats and other small craft.

Another object of the invention is to provide a continuous depth ilnder which does not require the use of motors, and includes novel means for measuring with a direct current meter, the time between the instant of transmission and the instant of receiving the first echo.

A further object is to provide an electronic echo sounding instrument which can be operated from a battery as the only source of power, and which involves the use of small vacuum tubes.

A still further object of the invention is to provide a novel 'electronic timer circuit for continuously indicating the depth of the water below a vessel which is moving or stationary.

In accordance with the invention, for example, there is provided a. portable instrument for the rapid, automatic determination of depths of water up to a maximum distance, such as 100 feet, for example, below an outboard projector comprising a pulse transmitter, an echo receiver, and means for indicating sea bed contour changes along the vessel's course. The instrument generates supersonic sound pressure waves having a constant frequency of 25.0 kc., for example, at a predetermined constant rate of twelve per second, for example; projects the pulses downward; times them accurately in units oi depth in their path of travel to the Sea bed and return, by reflection; and indicates the water depth directly in feet on a calibrated meter. Operation of the sounding indicator isL entirely automatic.

'Ihe accompanying drawing is a diagrammatic view of an echo sounding circuit exemplifying the invention.

The illustrated circuit includes a sounding lndicator l and an outboard projector P. The outboard projector P contains a magnetostriction type oscillator transmitter T and receiver R in the same housing. The transmitter T converts the generated electrical impulses into sound pressure waves and projects them downward to the bottom while the receiver R converts the reected sound pressure waves into electrical impulses. The outboard projector P is adapted to be swung over the side of the boat and positioned under the water line for observations.

'I'he sounding indicator I is housed in a box containing an instrument panel lil and an upper chassis l2 and a lower chassis It, all of which are arranged so as to be readily accessible. On the panel l0 are mounted a power switch Iii, which controls the power supply from a six volt battery I8 to the entire unit; a depth indication meter 20, which indicates the depth of water below the outboard projector directly in feet and is also used to check the battery and calibrate the instrument; a keying rate indicator 22, which indicates the sounding rate by a vibrating reed, for example; and a three-position test switch 2d.

The keying rate indicator 22 has five reeds, the center reed being designated by an arrow and the left and right outer reeds "slow and "fast," respectively, thereby indicating directly the keying rate per second by the vibration of a reed. By adjusting a keying rate potentiometer 2t onthe panel I0 and a potentiometer 28, on the lower chassis It, the keyingr rate may be adjusted precisely to the predetermined constant value in this case twelve pulses per second, which corresponds to maximum amplitude of the center reed. The keying rate potentiometer 26 provides for adjustment through rather narrow limits, additional adjustment being provided by the potentiometer 28. The keying rate should be accuratelyadjusted as any error in this adjustment ailects the depth readings in the same proportion.

The three-position switch 2d is of the spring return type, being normally in the depth position for depth indications. In battery position, the charge of the battery I8 may be checked on the meter 20. In calibration position, a calibration potentiometer 30 on the panel may be adjusted, so that the pointer is in exact alignment with a predetermined mark. This adjustment should also be very carefully made, as any error affects the accuracy of the soundngs in the same proportion.

The lower chassis it contains a vibrator plate power supply 32 for the unit; a blocking oscillator 3d, which initiates the electrical pulses; and a discharge circuit 36. The upper chassis i2 contains a. receiver-amplier circuit 38 and a tlming circuit All. 'I'.he plate power supply 32 is a separate chassis type unit mounted on the lower chassis. It contains a synchronous vibrator A2;

a transformer 44; and associated resistor 46. inductors 48 and 86, and capacitors 62, 64 and 66 for illtering` purposes. The output voltage of unit 32 is controlled by a voltage regulator tube` 86 for all component circuits except the discharge circuit 86.

The sending of pulses, or keying, is controlled by that half of vacuum tube 86, which is associated with transformer 62, capacitor 84, resistor 88, and potentiometers 28 and 20. These elements comprise the vacuum tube oscillator 64, which would normally oscillate at an audio frequency. The circuit is so designed, however, that in endeavoring to oscillate the grid 68 draws current, develops a high negative bias .and blocks itself. An impulse is transmitted each time this blocking takes place. The rate at which blocking occurs is adjustable by means of potentiometers 28 and 28 as previously described. Thus, by careful adjustment oi these two potentiometers,

the keying rate may be accurately Jset at 12 pulses I per second.

The other half of tube 60 amplifles these pulses and transmits them simultaneously to the grids and 12 oi a grid-controlled gaseous-discharge tube (strobotron) 14, and a gas-filled grid-controlled rectiiler tube such as a thyratron 16.

Each pulse on the grid 16 of tube 14 fires or` ionizes the gas in such tube, forming a conducting path from anode 18 to cathode 86 and thereby discharging a capacitor 82 through and energizing the transmitting projector T. The thyratron 16 controls the voltage on the screen 84 of a screen-grid amplifier tube 86 on the upper chassis I2. At the instant the pulse is applied to the grid 12 of thyratron 16. it ionizes the gas in such tube, and the plate current ow through thyratron 16 lowers the screen voltage on tube 86 by the IR drop through an associated plate and screen resistor 88. When tube 16 res, condenser 6 discharges through tube 16 and resistor 8, the condenser 8 and resistor 8 forming a delay network. At the same time the condenser 9 tends to recharge from the' positive side of the power supply through resistor 86 but the time constant oi the latter circuit is so adjusted with respect to the time constant of the circuit consisting of resistor 8 and condenser 6 that the discharge current exceeds the charging current and the anode potential of tube 16 is reduced to a point where the tube ceases to fire, the maximum current through the limiting resistor being insufilclent to maintain an arc in tube 16. When tube 16 ceases to fire condenser 8 is gradually charged through resistor 88 and the screen voltage of tube 06 is gradually returned to its original value, the time being determined by the time constant of the circuit consisting of resistor 88 and condenser 6. This drop of short duration in screen voltage reduces the gain of the receiver-amplifier 38 for said period of short duration so that a false indication of depth, due to direct transmission from the transmitting to the receiving projector. is avoided. 'I'he condenser 8 reacts on tube 86 in such a manner as to perform the functions of an automatic gain or volume control.

Crosstalk which would be indicated on the meter 26 as a steady very low depth reading regardless of the true depth of the water may be due to a variety of causes. such as, the direct transmission between transmitter T and receiver R. electrical coupling between the leads to the transmitter and receiver, reverberation in the housing of the outboard projector P and the like. For any particular installation, therefore. it is dll necessary to provide a control which will maintain the gain of tube 86 below a, level which would transmit crosstalk until the effects which produce such crosstalk have disappeared. To this end the potential of the cathode of tube 66 is made adjustable so that the relative potential between the cathode and screen grid. which relative potential constitutes the means for reducing the gain when signals are transmitted. may be varied tc accommodate various situations that may arise. This adjustment is provided by the potentiometer H6 in the cathode circuit of tube 86 which in adjusting the potential of the cathode with respect to ground likewise adjusts the relaf tive potential existing between the cathode and screen grid. By proper adjustment the relative potential between cathode and screen grid may be so regulated that this potential does not rise to a value that would permit signals to be ampliiied by tube 88 until after the conditions which would produce crosstalk have ceased. In other words, potentiometer H6 adjusts the gain level and hence the crosstalk threshold of tube 86. In practice an initial regulation of potentiometer H6 for any given installation is all that is usually necessary.

The three-stage receiver-amplifier 38 on the upper chassis l2 is tuned to a frequency of 25.0 kc., the natural period of the projectors T and R, b'y capacitors 80 to 88, inclusive. connected across the secondary |00 of an input transformer |02, and also by capacitors |63 and |04. connected across a second stage coupling inductor |06. Resistance coupling |08 is employed from the second to the third stage. The received electrical pulse, from the reflected signal or echo, is amplified by amplifier tube 86 (its screen voltage returning to normal, as determined by the product of the resistance and capacitance in the plate circuit of tube 16, before the echo" from deep water is received) and amplifier tube H0 and applied to the grid H2 of amplifier tube H4.

Tube H4 is biased beyond cut ofi'. so that any extraneous noises will not give false depth indications as several volts of signal are required for operation of the tube. The plate voltage of tube H4 is the same, with respect to ground, as the grid voltage of a grid-controlled space discharge device or vacuum tube i0 in the timer circuit 46. Therefore. as soon as tube H8 ceases to draw plate current, as described below, the plate voltage of the amplifier tube H4 is reduced to the extent that this latter tube is inoperative and even a very strong signal or any extraneous noises picked up by the receiver-amplifier 36 will not cause false operation of the timing circuit 60.

Grid-controlled space discharge devices such as screen-grid vacuum tubes H8 and |20 and their immediately associated circuit elements, constitute the time measuring or trigger circuit 40. They measure the ratio of the time necessary for a pulse to be transmitted to the "bottom and be reected back to the receiving projector, to the time between pulses. A potential of plus volts D. C., with respect to ground, is applied to the screens |22 and |24 of tubes H6 and |20, and also to the ljunction |26 of resistors |28 and |36. The other end of resistor |28 is connected by conductors |32 and |34 through meter 26 to the plate |86 of tube H8. The other end of resistor |36 is connected to the plate |38 of tube |20. Resistors |40 and |42 are connected in series circuit relation between the plate |38 of tube |20 and ground |44, the grid |46 of tube H8 being connected to their junction |48, and thus this grid itt is positive with respect to ground. In a similar manner resistors |50 and |52 are in series between the plate side of resistor |28 and ground |02, and the grid |60 of tube |20 is connected to their junction |06. so that this grid |06 is likewise positive with respect to ground.

` Plate and screen currents of both tubes H and |22 iiow through the "calibration" potentiometer and a resistor |52 to ground it, so that the cathodes |50 and |82 of both of these tubes are also positive with respect to ground. Thus a trigger circuit t0 is provided, which permits only one of the plate or output circuits of tubes lid and |20 to draw current at a time. The resistor itt is used to stabilize the voltage of cathodes |160 and |62 of tubes H2 and |20. The grid of the other tube is biased beyond cut od until some disturbing voltage, such as that resulting from the transmitting pulse or the echo, upsets the balance and then the other tube draws plate current while the first is biased od. The potentiometer is variable so that, when the tube H0 is drawing current, its plate current may be ad- `iusted to a certain steady value, in this case two miiliamperes. At all times the grids |00 and |06 of tubes and |20 are negative with respect to their cathodes |00 vand iB2.

When the instrument is in operation, tube |20 draws current during the short interval between receipt of the echo and the sending out of the next pulse and its grid IM is slightly negative with respect to its cathode |62. At the same time, due to the IR drop through resistor |30, the grid voltage of tube llt is so low that this tube is biased beyond cut off and draws no plate current. Also the plate voltage of amplifier tube |2 (which voltage is the same as the grid voltage of tube I0) is so low that all signals are effectively prevented from passing to the grid |26 of tube H8.

'I'he grid |52 of tube |20 is coupled to the anode it of the gas-filled tube 1t on the lower chassis it by means including capacitor |62 and resistors it@ and |58 so that a pulse on the anode 18 of tube 1t is impressed on the grid |50 of tube |20. This pulse, being amplified by tube |20, reduces the bias on the grid It@ of tube ||8 so that this tube ||8 begins to draw current. Due to the resulting IR drop through resistor |28, the voltage on the grid |50 of tube |20 is reduced so that this tube |22 is biased beyond cut oif and, therefore. ceases to draw current. The amplied received impulse, or echo" is impressed on the grid |I|2 of tube iid, overrides its bias and since its plate voltage is normal the tube draws current. The echo pulse then passes to the grid |06 of tube H2, is amplified by such tube and impressed on the grid` |52 of tube |20. The pulse reduces the grid bias on tube- |20, and the tube |20-begins to draw current immediately. Tube H8 then is immediately biased ofi, as previously described. and ceases to draw current. Thus, the circuits are established for the next pulse from the anode 18 of tube 1t.

At the instant tube I8 begins to draw current,

age value is l milliampere, for 50 feet it is 0.5 milliampere, etc. The meter 20 is specially designed so that it gives a steady reading of this average current on a scale calibrated directly in terms of depth such as feet.

The transmitting projector T converts electrical impulses received from the discharge of capacitor B2 in the sounding indicator I, into sound pressure Iwaves, which pass through the water to the bottom and are reflected back to the receiving prolector R. Each projector consists of a stack of toroidai nickel laminations, wound with wire through which the electrical impulses pass. Each pack is housed in a conical reflector, which is lledwlth castor oil and sealed by means of a diaphragm and suitable gasket against leakage.

The electrical impulses set up a magnetic field in the laminations of the transmitting projector, causing the nickel to contract las the field increases and expand as the fielddecreases, thus setting up mechanical vibrations or sound pressure waves, which are transferred to the castor oil within the conical reflector. This effect is known as magnetostriction- These pressure waves are I then reflected, by the conical reflector, in a parallel-vertical beam; travel through the diaphragm to the bottom where they are reflected back to the diaphragm of the receiving projector. The received sound pressure waves reach the conical reflector surrounding the receiver pack and are deected to the pack to set up vibrations within the nickel laminations.

The receiver pack diiiers from the transmitter pack in that it should be pre-magnetized by a momentary impulse of direct current. Vibrations set up by the sound pressure waves cause contraction and expansion of the pack, a change in the magnetic field and thus an electrical impulse is generated in the pack winding. This electrical impulse is then transmitted to the primary |10 of transformer |02 in the sounding indicator I through the inter-connecting wiring |12.

The natural frequency of both packs may be 25.0 kc., which is outside the frequency of interfering noises, such as those caused by chang objects and the like.

Operation of the unit is entirely automatic, requiring only the switching on of the power and an occasional check of the keying rate and calibration. A pulse, generated by the blocking oscillator 34, ioniaes the gaseous discharge tube (strobotron) 1li, thereby discharging the capacitoi` 82 through the transmitting projector T and initiating the sound pressure wave. The reflected Wave, or echo reverts to an electrical impulse, by virtue of the action of the receiving projector R, is amplified by circuit 38 and translated, by means of electronic timing circuit 00, into a reading of the depth in feet on the depth indication meter 20 in the sounding indicator I.

The principle of operation of the invention has been described, together with apparatus which now is considered to represent the best embodiment thereof, but it should be understood that the apparatus shown is only illustrative and that the invention may be carried out by other means. Certain features of the invention which are believed to be novel and patentable are defined in the following claims and other inventive features are claimed in the copending application of Fred L. Seeblnger, Jr., entitled-Echo sounding indicator, Serial No. 582,149, led March 10, 1945.

I claim; 1. In an echo sounding indicator, a reflector containing two magnetostriction oscillators one for transmitting a pulse when energized and the other for receiving the echo of such pulse, a pulse transmitter circuit comprising a capacitor, a direct current charging circuit connected to said capacitor, a grid-controlled gas-filled rtube adapted when' fired to dischargesaid capacitor through the pulse transmitting magnetostriction oscillator, an electronic oscillator coupled to said tube for ring the tube at a predetermined uniform rate such that the interval between pulses is suilicient to allow the first echo of each pulse to be received before the next pulse is transmitted, means for adjusting the firing'rate of said tube. and a frequency meter connected to indicate such firing rate, a receiver amplifier circuit the input of which is coupled to the echo receiving magnetostriction oscillator, a timing circuit comprising two grid-controlled space discharge devices. the input circuit of the first device being coupled to said capacitor and the input circuit of the second device being coupled to the output of said receiver amplifier circuit, a network of resistors connecting the input and output circuits of said devices so that a trigger circuit is provided and direct current flows in the output circuit of the second device only during the time interval between the instant a pulse is transmitted and the instant the first echo of such pulse is received, and a direct current measuring instrument calibrated in.x terms of depth and responsive to the average value of such current over a series of such successive intervals of time, and a coupling between said receiver amplifier circuit and said second device comprising a. grid-controlled vacuum tube the grid of which is normally biased a little beyond cut-off to prevent accidental operation from noise, the plate voltage of said vacuum tube being derived from said timing circuit in such a. way that such voltage is at a maximum value until an echo pulse has been received, whereupon such voltage drops to a minimum value, providing protection against accidental operation by echoes other than the rst.

2. An echo-sounding indicator comprising, in

iii ii" combination, means for electronically generating and transmitting pulses at a regulatable constant frequency and fixed rate, means for receiving echoes of the transmitted pulses, means for timing the intervals between the transmitted pulses and the first echoes thereof including a pair of grid-controlled devices .having their grid and plate electrodes interconnected through a network of resistors to provide a trigger circuit in which current flows in the plate circuit of only one of said devices at a time, a coupling circuit connecting the transmitting means to the input circuit of the first of said pair ofl grid-controlled devices, a coupling circuit connecting the receiving means to the input circuit of the second of said pair of grid-controlled devices, said last mentioned coupling circuit including a discharge tube, a connection between the plate of said discharge tube and the plate circuit of said rst of said pair of grid-controlled devices whereby when plate current nows in the plate circuit of said first of said pair of grid-controlled devices the plate potential of said discharge tube is reduced to such an extent that the tube is inoperative and even a very strong signal or extraneous noise picked up by the receiver will not be transmitted through said tube to said second of said pair of grid-controlled discharge devices to cause false operation of said timing means, and an indicating device connected in the plate circuit of said second of said pair of grid-controlled devices.

GEORGE T. IDRANCE.

BEFERENCEB UIT The following references are of record in the ille of this patent:

UNITED STATES PA'IENTS Date OTHER REFERENCES Reich, Trigger Circuits," in Electronics for August 1939, pases 14-17 inclusive.

Reich and Tocmin, Electronic Circuits for Measuring Time and Speed. in the Review of Scientific Instruments for December 1937, pages 502-4 inclusive. 

